1. Field of the Invention
The present invention relates to a method of preparing specific esters of acrylic acid and methacrylic acid (said acids hereinafter designated collectively as "(meth)acrylic acid"). More particularly, the invention relates to esters of higher alcohols and of substituted alcohols other than polyhydric alcohols, said method starting with esters of acrylic and/or methacrylic acid with alcohols having 1-4 carbon atoms, which esters are available from large scale industrial sources, and said method employing metal compounds as catalysts.
2. Discussion of the Background
The catalytic action of inorganic bases in many transesterification reactions is well known (Swiss Pat. No. 239,750). This base-catalyzed reaction is employed advantageously to prepare higher (meth)acrylic acid esters or basic esters from methyl and/or ethyl esters of (meth)acrylic acid (Ger. As 11 80 527; U.S. Pat. No. 2,138,763; G. D. Graves and M. B. Horn in "Acrylic Resins", Reinhold Publ. Corp., N.Y., 1960). It is clear from the literature that effort in the art has been concentrated on solving specific problems of the application of particular catalysts.
In one known prior technique of transesterification, methyl methacrylate is reacted with tetraethylene glycol in benzene in the presence of sodium hydride as described in JACS, 77, 194 (1955). The methanol formed was removed by distillation as a benzene-methanol azeotrope.
The transesterification reaction of methyl acrylate and/or methyl methacrylate with dialkylaminoalkanol in the presence of calcium hydroxide or calcium oxide is disclosed in Japanese Laid Open Application No. 75-142,513 (see CA, 84, 136271f).
Catalytic acceleration of the transesterification of methyl methacrylate with, e.g., 2-ethylhexanol, by a lithium compound such as lithium hydride, alkyllithium, phenyllithium, lithium aluminum hydride, lithium borohydride or an alkoxide of lithium borohydride, lithium salts of organic or inorganic acids, lithium acetylacetonate, lithium oxide, or lithium metal, is disclosed in Jap. OS No. 79-41,815 (CA, 91, 40095v). Particular interest has been shown in the transesterification of lower esters of (meth)acrylic acid with glycidol to form glycidyl esters. The transesterification of methyl methacrylate with glycidol in the presence of alkali hydroxides, or alkali carbonates, -sulfides, -polysulfides, or -thiosulfates, lithium halides, or sodium-, potassium-, rubidium-, or cesium iodides is the subject of Japanese Laid Open Application No. 80-94,378 (CA, 94, 121290u).
Transesterification of methyl (meth)acrylate with glycidol in the presence of alkali halides, particularly lithium chloride, to yield glycidyl (meth)acrylate, is described in Japanese Laid Open Application No. 80-105,676 (CA, 95, 121292W), while Japanese Laid Open Application No. 80-127380 (CA, 95, 7026h) discloses the transesterification of lower esters of other organic carboxylic acids with glycidol in the presence of alkali halides, particularly sodium bromide.
In the art there is a recognized need for, in addition to (meth)acrylic acid esters such as methyl methacrylate, which are produced on a large industrial scale, additional specialty esters which, e.g., enable modification of the polymer properties or the production of special polymer systems (see H. Rauch-Puntigam and Th. Voelker, "Acryl- und Methacrylverbindungen", Springer-Verlag, 1967)), J. Brandrup and E. H. Immergut Ed., "Polymer Handbook" 2nd Ed. J. Wiley & Sons 1975.)
The progress made by those skilled in the art toward solving the specific problems of preparing special esters of (meth)acrylic acid has been in the area of devising specific transesterification catalysts. In the interest of a maximally integrated technology, however, there is also a need for a method, which should be generally applicable, to improve product quality and yield without having to make any ecological or economic concessions. Two other factors beside ecology and cost which add to the difficulty of the problem are the risk of polymerization (when esters of polymerizable acids are employed) under the conditions of the reaction and/or subsequent processing, and the side reactions which occur. Further, ester interchange with certain alcohols present special problems.
A particular aspect of the above-stated problem is to influence the transesterification of esters of carboxylic acids such as (meth)acrylic acid, which acids can polymerize by radical polymerization, said interchanges involving specific alcohols, such that one maximizes the degree of the transesterification, i.e. achieves high yields with maximum selectivity.
The state of the art gives no indication or hint of the fact that a catalyst system comprised of different components, which are individually relatively inactive, can exhibit a synergistic action in transesterification reactions according to the previously stated underlying problem of the invention.